Metallic containers or cans have widespread use for the packaging of beverages, especially beer and soft drinks. Originally, these can bodies were produced from a tube which was formed from flat sheet steel, which tube was interlocked, soldered and/or welded along a side seam and included a first end member seamed to the tubular body prior to filling thereof and a second end member sealed thereto after filling thereof.
More recently, the three-piece can body previously described has been supplemented with the two-piece can body. In such a two-piece can body, a circular blank is cut from a metallic sheet. This blank is then drawn into a cup-like shape. The cup may then be redrawn into a final inside diameter. Whether or not the cup is redrawn, it is then ironed between a punch over which the cup is carried and one or more ironing dies, with the dies having a diameter slightly less than the outside diameter of the cup. This ironing produces a thinned and lengthened sidewall. Finally, the bottom of the now ironed can body contacts bottom forming tooling which, in cooperation with the end of the punch over which the can is carried, forms a bottom structure taking one of numerous forms. The completed can body then has a single end element seamed to its open end after filling.
As can easily be realized, while the major length of the sidewall of the can body has been thinned by the ironing process, the can bottom structure retains substantially the same wall thickness as the original sheet material from which the blank was formed. This bottom structure must withstand bulge pressures after filling and sealing of the can under the pressure provided by the beer or soft drink retained therein in excess of 90 lbs. per square inch (63279.0 kilograms per square meter). Additionally, this bottom structure must help provide column load strengh to the can body, which column load strengh must exceed 350 pounds (158.7 kilograms).
The weight of the metal employed to produce the can body is a substantial portion of its cost. These costs are reflected in direct metal costs, shipping costs and the like. Thus, it is desired to form can bodies to be as light as possible, while retaining the required strengh to prohibit failure of the can. Since a substantial portion of weight in a can body is in its bottom portion, and since the bottom portion is determined by its base structure and the thickness of the metal in this region, it is desired to form can bodies having base structures capable of withstanding the required bulge pressures and column load forces while using as thin a metal blank to form this can body as possible. Thus, it is a primary objective of the present invention to produce a can body having a bottom structure capable both of withstanding bulge pressures in excess of 90 lbs. per square inch (63279.0 kilograms per square meter) and column loads inn excess of 350 pounds (158.7 kilograms) while being formed of the thinnest possible sheet material.
An additional weight savings in forming a can body may result from the use of the smallest possible circular blank. A can body must have a specific height, with the height being determined by the volumetric capacity of the can being produced. The height of the sidewall is determined primarily by the amount of metal in the sidewall of the cup from which the can body is formed and by the amount or ironing to which the sidewall is subjected. However, reductions in the amount of metal necessary to form a required sidewall height can also be accomplished by producing a bottom structure which requires less total metal to be taken from the sidewall during its formation than previously required. In such cases, less metal from the sidewall is moved to the bottom structure when forming the bottom structure, thus reducing the height of the sidewall in a lesser amount than previously required. By controlling this metal movement, it is possible to produce a can body with the sidewall being somewhat shorter than previously necessary. This then permits the can body to be formed from a metal blank of somewhat smaller diameter than previously required, thus once again reducing the total metal usage for the can body and thus the cost of the can.
It is thus also a primary objective of the present invention to produce a can body having a bottom structure which requires less metal to be taken from the sidewall as it is formed than previous bottom structures.